The Fermi Paradox Explained: Here's Why Alien Life Hasn't Found Us Yet

As NASA announces a new planet and a spacecraft careens past Pluto, humanity is getting closer to discovering whether or not it's alone in the universe.

Space is, after all, busy these days. We've seen our icy dwarf planet closer than it's ever been observed, and a newly discovered planet, Kepler-452b, is one of a billion planets in our galaxy that could support life. Based on a process called the Drake equation, there could be around 100,000 civilizations in our galaxy, never mind the entire universe. On some distant Earth-like planet, there could be a dive bar that looks like the cantina scene in Star Wars Episode IV: A New Hope.

So why haven't we been contacted by another civilization? Why is it that, when we look up in the sky on a clear, block-party-barbecue night, all we see are planets and stars but no signs of life beyond the ones flung up there from Earth?

Plenty of theories exist — which is how we know there's no actual answer. At least, not yet.

In 1950, when Italian physicist Enrico Fermi posed that question, it became known as the Fermi paradox. His grand speculation: If the universe should be full of sophisticated races and civilizations, why the hell do we feel so alone?

If the universe should be full of sophisticated races and civilizations, why the hell do we feel so alone?

Which, when you think about it, makes a lot of sense. Think of Pluto, how long it took to get there and the fact that it revolves around the same sun we do. Everyone's favorite heart-tattooed dwarf planet is, at its closest, still over 2 billion miles from Earth. Now, keep in mind our sun is one of the roughly 200 billion stars (on the super conservative end) in the Milky Way galaxy. Take another step back to see the Milky Way galaxy is just one of the roughly 100 billion galaxies (again, conservative figure) the Hubble telescope helped estimate.

So, sure, the universe is beyond huge, and it would take millions (if not billions) of years to explore. But if the universe is 14 billion years old, then, hypothetically, aliens could have already found us. So what gives?

There are several moving parts to the Fermi paradox, and the first revolves around the concept of the Great Filter.

In 1998, an economics professor named Robin Hanson wrote an essay called "The Great Filter — Are We Almost Past It?" in which he detailed humanity's evolutionary path. The "filter" here refers to the idea that each evolutionary step, from having the right star system to sexual reproduction to multicellular life to colonizing the universe, comes with a barrier that needs to be crossed. And as a civilization approaches a barrier and attempts to cross it, the probability of perpetuating life gets smaller.

"Since we don't see civilizations out there, well the path from bacteria to civilizations must be hard," Hanson told Mic. "It's the step ahead we're unsure about. The steps we haven't gone through. That raises the chance that the hard parts are ahead."

There are three groups of thinking on this theory. The first is commonly called the Rare Earth Hypothesis: Humanity has already passed the Great Filter, something no other race has been able to do, and now we're alone in the universe while all other species die before they can pass it.

The third and most depressing possibility is that the Great Barrier is ahead of us, there's at least one more barrier before we can become an advanced civilization and it's extremely unlikely we're going to figure out how to do that. But other races may have.

If astronomers are correct about the universe's age, that means Earth wasn't even a planet for almost 10 billion of those years. A great site called Wait but Why drew up some charts to illustrate the expanse of time another planet — in this case, the hypothetical Planet X — could have existed and thrived in that time.

If 3.46 billion years of development is unfathomable, here's some perspective: That tiny orange bar on the chart above represents 65 million years. That's only 65 million years between Jurassic Park's reptilian antagonist dying off and the iPhone 6. If humanity was able to go from fleeing Sue to palm-sized computers in that time span, imagine what another developing race could accomplish with 3 billion extra years.

That all assumes intelligent life evolved at the same rate — or evolved at all.

The Kardashev scale is a measurement of where civilizations exist in their technological advancement. It's said Carl Sagan estimated humans hadn't even hit this level, but that we're closer to a Type 0.7 civilization. The barrier we're staring at right now is fully harnessing the power of the planet, which we may not hit for another 50 to 100 years.

The next step up would be a Type II civilization, which could theoretically harness the power of their star, creating what's called a Dyson sphere, a megastructure capable of tapping into all the energy the sun gives off and using it as a power source. The most badass type of civilization is Type III — a godlike, omnipotent, galaxy-harnessing advanced race that could pretty much do whatever the hell it wanted.

"I did a TED Talk in 2014, but I've thought of this a bit more since then," Hanson told Mic. "One new twist that I haven't appreciated this well before is the idea that filters could be smooth or lumpy. Smooth filters would be where everything is a little hard, and the total difference adds up to a lot, and that's bad news because it would mean there are a lot more steps to go through. A lumpy filter is what we should hope for."

Imagine a large hill on one end of the evolutionary path. "That means the hard things are all in one or two places. It could be that we're past all the filters, and [after] you already have the origin of life, it's smooth sailing."

Of course, some civilizations may have already hit and triumphed over those barriers. But that still doesn't mean communicating is going to work.

Advanced civilizations might be out there, but there are plenty of reasons they won't pick up the phone.

"We've only been listening for other civilizations for 50 years," Bill Nye said in a Big Thinkinterview. "You have to acknowledge that civilizations have to emerge and be able to communicate at the same time. If you have something that's been going on for 13.6 billion years, there's a lot of opportunities to miss each other."

Even if an advanced civilization came groping around our corner of the darkness in search of intelligence, human life on Earth is so young that they could have been here when Earth wasn't even a glimmer in the universe's eye.

Considering how infantile humanity is when it comes to communicating, there might be entire galactic conference calls going on that we don't have the technology to hear or interact with. Or, advanced life may know we're trying to communicate, but after seeing we're essentially using a soup can on a string to call the International Space Station, would just ignore us and watch us grow before trying to initiate a conversation. That watching bit, as you might expect, is called the zoo hypothesis.

Really, here, the options are endless: The universe could be mostly colonized and heavily populated already — but light-years away from our rural backwater of space. They might be completely content with their own level of technology and don't want to spend the resources jetting off into the nothingness if their planet isn't getting used up at an alarming rate. And then, of course, our Napoleonic view of civilization might be so far in their past that physically searching for things is antiquated, and they all live in a virtual simulation of anything they could possibly ask for. What's more, the universe itself could be a hologram, and we'll never see what's on the other side of it.

Then, of course, there might be civilizations who are not just minding their own businesses. Finding them could be really, really scary.

Why we should be terrified if aliens ever attempt to contact us

As a race, we're so egocentric that we believe we must be super smart, or at least would get along with the super-smart civilizations at parties. But what's more possible is, to a hyper-intelligent race, we're the bugs that live on a bunch of natural resources. So if there are races out there trying to colonize the galaxy or mine for resources, they might not necessarily want us dead. We're just the casualties of planet mining.

Or they might actually be totally menacing and, assuming we're getting really close to the next barrier on the way to higher intelligence, they might come along to blow us out of the sky, which is part of why Stephen Hawking wants us to knock this off.

"We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet," Hawking said in a Discovery Channel series, according to Popular Science. "If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans."

Which addresses another theory: We don't see anything out there because other civilizations are hiding from one predatory race decked out in advanced technology and trying to colonize the galaxy.

"That's troubling because why would it be hiding?" Hanson said to Mic. "They're powerful and can make things. Hiding is expensive because you're setting aside resources. If you want to tell the story like that, they must be hiding for a very good reason. If it was just [one other race] out there, then they wouldn't need to hide. And if they aren't hiding, then it must be much easier for them to squash something than to find something that does the squashing."

But we shouldn't give up hope.

Stephen Hawking is an irrefutable genius and a total buzzkill. The theory he espouses seems unlikely. If an all-powerful race in the universe was going around and stomping out the flames of progress, chances are it would have found us by now. We shouldn't be turned off by hyper-fatalist beliefs or the idea that we should stop trying since we haven't found anything yet.

"For me the Fermi paradox drives us forward," Nye said, according to Big Think. "Why haven't we heard from anybody? Because we aren't listening hard enough. We aren't being diligent enough. ... One way to be sure you never hear from another civilization and realize or validate Fermi's paradox is to not listen. To me this is an obligation of a civilized society."

We know almost nothing about what's going on in the vastness of space. And besides some of the very limited scientific knowledge we've developed so far, it's mostly speculation, theory, philosophy and astronomy. But it's hard to look up at the sky, knowing, even on the clearest night, that we're seeing only a hundred millionth of the stars in the Milky Way.

And if we're already beginning to find Earth-like planets in the 90 billion light-years of space, this might only be the beginning of a very cool future.